then uncomplainingly takes ten years off to stay at home with the kids because—as she explains it—that's just the way life is, and sensible women just try to keep up with the professional literature in their spare time. I know this is going to make me sound like a shallow and trivial person (which I am), but I spent a distressing amount of time wondering just how apocalyptically bad this couple's sex life was.... Honestly, though—who cares about all that? This is a genuine Frederik Pohl and Arthur C. Clarke novel. It's a worthy addition to both men's works. And, best of all, it's a chance to sit down one more time with a pair of old, old friends and find them just as sharp, witty, and wise as they ever have been. * * * * I haven't been paying enough attention to Greg Bear lately. In theory he's one of my favorite hard sf writers. But lately he seems to have abandoned sf in favor of mainstream-ish near-future technothrillers. And reading airport books by Greg Bear is sort of like listening to Glenn Gould play the Boston Pops. He writes them so well that it seems downright churlish to complain. But for cripes sake...doesn't the guy who wrote Slant and Blood Music and Queen of Angels have better things to do? Or anyway, that's my excuse for letting City at the End of Time languish unread on my desk for several months before I got around to looking at it. What was I thinking? City at the End of Time is about the furthest thing in the multiverse from an airport novel. It's also true hard sf. Reviewers who've characterized the book as Miéville-esque urban fantasy haven't just missed the boat—they're still staggering around in the fog trying to find their way down to the water. In essence, this book is a vast, oceanic riff on Jorge Luis Borges's “Library of Babel.” Bear is not the first writer to pen a meditation on this seminal story. However, this is the only “Babel” variant I can remember that has enough intellectual and emotional muscle to read like an independent story, rather than a mere retelling. It all begins with a map, natürlich . Thus far we are still in the domain of fantasy. But this is not one of those “worlds with square corners” maps that Ursula K. Le Guin likes to make fun of. Instead, it is a forbiddingly abstract set of interlocking circles: a cryptic image that challenges readers to produce their own explanations. On first seeing it I wondered if it might represent a mitochondria's eye view of the world outside the sheltering cell walls. Or perhaps the sort of inside-out, topsy-turvy cosmology that might be conceived by beings that inhabit the mantle of a star? Or, maybe...well, my other speculations were all even more embarrassingly off target. The map is a tease, of course. But Greg Bear is an honest tease—as are all great writers. He keeps the mystery alive not by stingily withholding information but by presenting rich, vivid, wonderfully polyvalent clues that challenge readers to come up with new hypotheses and test them against the unfolding story. It is a gauge of Bear's mastery that the book never feels like a cheat and that he manages to craft a reading experience that blends the rigors of scientific method with the more homespun pleasures of good gossip. The reading experience was not wholly gripping on a page-by-page level. At least not for me. But slack moments are inevitable in a long novel whose core subject matter has more to do with quantum physics than human emotions. And when I did catch myself skimming it was almost always because I was impatient to find out what was happening in the other storyline. That says volumes. I also felt another kind of impatience while reading this book—one that is characteristic of the experience of reading really great hard sf. I wanted to know what Bear was after . I wanted to get to the end of the book in order to be able to look back and take stock of the whole territory. And not just the territory of this particular book.